In the manufacture of photographic films and papers, a support is commonly coated with multiple layers. The different layers have different individual functions in the final product, and in many instances it is necessary that the layers remain distinct and not mix with one another. For example, a simple color photographic film can have a subcoating, a blue-sensitive layer, a green- sensitive layer, a red-sensitive layer, one or more color filtering coatings, etc. Films with about 15 layers have been described, e.g. in EP 257,515, herein incorporated by reference.
In forming photographic elements, the layers can be applied to the support by various procedures known in the art. For example, the layers can be applied by dip coating, roller coating, spray coating, bead coating, and the like.
Two or more layers can be simultaneously applied as illustrated by U.S. Pat. Nos. 2,761,791, 3,508,847, 3,539,644, and such other patents cited in Research Disclosure No. 308, December 1989, pp. 1007-8 herein incorporated by reference. There, coating and drying procedures are discussed.
High purity gelatins are generally required for imaging applications. Currently the manufacturing process for obtaining high purity gelatins involves demineralization of bone, followed by extended alkaline treatment (liming) and finally gelatin extraction with water of increasing temperature. This process commonly referred to as alkaline processed ossein has existed with various modifications throughout the gelatin industry for a number of years. The liming step of this process requires up to 60 days, the longest step in the approximately 3 month process of producing gelatin. The extended time required by the current limed ossein process for producing gelatin results in the need for increased inventories of the gelatin product. U.S. Pat. No. 4,824,929, incorporated by reference herein describes a suitable process for demineralizing bone.
This invention describes a novel process for the production of high purity gelatin utilizing the action of proteolytic enzymes for extraction of gelatin from demineralized ossein. The enzyme method of manufacturing gelatin described here produces gelatin with very low color and high gel strength over a wide range of viscosities. This high purity enzyme extracted gelatin is produced with a dramatic reduction in gelatin manufacturing cycle time due to elimination or shortening of a liming step. Further, the low temperature enzyme method of manufacturing gelatin results in lower unit manufacturing costs due to increased yield, reduced chemical costs, reduced water usage, and reduced utility costs.